The present invention relates to an image processor.
Recently, imaging elements having over one million pixels, such as a charge coupled device (CCD) and a CMOS image sensor (CiS), are being used in image processing systems such as digital cameras. Thus, high-speed data transfer is required for an image processor and a signal processor that processes the image data output from the imaging elements.
Generally, an image processing system includes a camera module and a base band LSI. The camera module includes an imaging unit, which includes imaging elements and generates image data for the three primary colors (RGB), and an image processing LSI, which converts the image data to image data in luminance/chrominance (YCbCr) format. The base band LSI compresses the image data output from the camera module to generate compressed image data and stores the compressed image data in the image memory.
The volume of data processed by the image processing LSI and the base band LSI, respectively, and the volume of data provided from the image processing LSI to the base band LSI increase as the number of pixels of the imaging element increases. The transfer time of data affects the time necessary until the next photograph can be taken (photographing interval).
One method for shortening the transfer time is to raise the transfer speed between the image processing LSI and the base band LSI. The frequency of a clock signal used for transferring data between the image processing LSI and the base band LSI is increased to raise the transfer speed. However, the employment of an interface enabling response to a high frequency clock signal for the image processing LSI (and base band LSI) increases the cost of the LSIs.
Japanese Laid-Open Patent Publication No. 2000-078513 describes another method for shortening the transfer time. In this method, the image data is compressed in compliance with the Joint Photographic Experts Group (JPEG) format with an encoder arranged in the image processing LSI to reduce the volume of data transferred between the image processing LSI and the base band LSI.